1. Field of the Invention
The present invention relates to protection circuits and more particularly to diode arrays used for protecting data processing systems.
2. Discussion of the Related Art
In data processing systems, connectors are often coupled to a large number of lines, the voltage of which is liable to vary between first and second states corresponding to first and second voltages.
The case where the first voltage corresponds to ground and the second voltage is a positive voltage, for example +5 volts, will be more particularly considered. But it will be understood that more generally, the voltages of these lines can vary between a high voltage and a low voltage, or reference voltage.
FIG. 1 shows a conventional protection circuit for a line of this type. Line L is connected to the reference voltage (or ground) through a reversely biased diode (d1) and is also connected to ground through a forward biased diode (d'1) in series with a reversely biased avalanche diode (Z) having a voltage close to (slightly higher than) the high voltage on the line. Thus, a negative overvoltage on line L flows to ground through diode d1 and a positive voltage, having a value higher than the nominal voltage of the line, flows through diode d'1 and the avalanche diode Z.
In data processing systems, a very large number of lines are coupled to a connector and it is necessary to combine various protection components such as the one of FIG. 1, all sharing a single avalanche diode. Such a circuit is illustrated in FIG. 2, where is shown, in association with each line L1-L8, a diode d1-d8 reverse-biased connected to ground and a diode d'1-d'8 forward-biased connected through an avalanche diode Z to ground.
In practice, it has been noted that it is more advantageous to select for diodes d1-d8 and d'1-d'8 Schottky-type diodes so as to decrease as much as possible the capacitance between each line and ground, and therefore to minimize the crosstalk phenomena liable to occur between two or several lines. Additionally, such small-size Schottky diodes have a relatively low forward voltage drop, hardly higher than that of a conventional junction diode.
Presently, this type of circuit is implemented with discrete components. This involves a cumbersome structure and expensive labor costs to carry out the various soldering operations required for production of the circuit. These are conventional drawbacks of discrete components as compared to an integrated component. Yet another drawback is that the small-size Schottky diodes are fragile components and very sensitive to reverse overvoltages that are liable to destroy them. Therefore, the circuit must be manufactured and connected with the greatest care so as not to impair or damage its elementary components.